i had no problems buying old glass. i had the Minolta 35-70 F4, Beercan and 50mm F1.7 a couple of Sigmas and a couple of Magnicons.
only got the Beercan cause i wanted to own a piece of the legend. it was a good sharp lens but i barely used it and it was also fairly slow to focus since it did not have limiter.
the 35-70mm and 50 F1.7 were sharp but later discovered they were both badly back-focusing.
then i got the Minolta 28-135mm lens and knew exactly what i was getting and the ebay seller guaranteed against any defects. i also knew it had a scratch on it's front element. it is a superb lens but if you shoot in the day, the sun has to be behind you or you get a nasty flare and also the MFD is pretty bad.
after getting the 28-135mm, i realized the Beercan could not even come close t match it. so i decided i needed a modern lens and bought the Sony 70-300mm G SSM and i love it dearly although i have not been able to use it much now that i have a new breathing toy :-)
i was also planning on getting the Sony 50mm F1.4 alongside with the G then decided against it and bought the Minolta 50mm F1.4 that Don offered me. pretty much the same lens optically just with a digital coating and ADI capabilities.
so basically what i learned from this is that the crappier your first few lenses are, the more you have doubts about the system as a whole or the body in specific.
if you buy a used lens, make sure the seller has some kind of guarantee against defects.
i also learned that bouncing flash makes a whole lot of difference in sharpness, colour and overall feel of the subject!
One problem for me was that when I started, I thought I wanted to get a camera that would be a step above a super-zoom. I wanted a little bit better image quality and low light capability, and thought the ability to control depth-of-field was handy. But that wasn't the case. I got my first taste and I was hooked. And now here I am, a few thousand dollars later.